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Re: [lvm-devel] [PATCH]: Enable snapshots of mirrors

On Oct 22, 2009, at 2:45 PM, Alasdair G Kergon wrote:

On Thu, Oct 22, 2009 at 01:54:21PM -0500, Jon Brassow wrote:
- commands ignored

pvmove is the only one to test I think and it ought to be OK, still
refusing to let you manipulate any devices concerned.

yup, pvmove skips over the mirrors and the snapshots of the mirror.

+ seems to work, but I didn't try corrupting the VG

vgck already gives incorrect exit status anyway, someone pointed
out this week...

- other vg commands/options ignored

I'd want to know that vgmerge and vgsplit always behave correctly and
understand the entire 'stack' of objects must remain together and give
sensible error messages/deal with name conflicts properly in the various
different cases.

vgsplit does not allow PVs with mirrors or snapshots to move - "Can't split mirror/snapshot between two Volume Groups", but it does allow other PVs to move.

vgmerge allows VGs with and without snapshotted mirrors to be merged into VGs that do and don't have other LVs.

+ '-an' of mirror properly shuts down snapshots too
+ '-ay' of mirror properly starts up snapshots too
+ '-a[ny]' of snapshot gives proper error message
+ '--resync' of mirror origin properly resync's it
- other options ignored

check permissions-handling too and --refresh and readahead setting

cursory check of --refresh shows it to work.

+ can't change RW permission of LV under snapshot
+ can change RW permission of snapshot

- largely ignored because I'm not familiar with normal output... but it
seems fine

Well, simply, can you easily tell how things are set up from its output,
or does more descriptive text need to be added?
(E.g. instead of saying just 'snapshot', saying 'snapshot of mirror')

It just says it is the source of snapshot 'foo' - nothing about mirror, but when I remove the snapshot, it doesn't say anything about it being mirrored either.

Most of this code was written with stacked devices in mind, but this is the first time we'll actually be turning on and using these code paths.

Sure. Let me know if you are satisfied with this basic level of testing, and I will check it in.


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